Point remote compaction tests at the mock ChatGPT server (#49114)

Set `chatgpt_base_url` to the supplied mock server URI in
`make_remote_compaction_session`.

GitOrigin-RevId: de5c6e208fd104cbe07a8873e7e33c108dac7a57

codex-rs/core/src/session/tests.rs

@@ -11581,6 +11581,7 @@ async fn make_remote_compaction_session(
         move |config| {
             config.model = Some("gpt-5.2".to_string());
             config.model_provider = provider;
+            config.chatgpt_base_url = server_uri.to_string();
             let _ = config.features.disable(Feature::TokenBudget);
         },
     )